This invention relates to an improved spacer clip and is particularly directed to a non-conducting spacer clip adapted for mounting on header bars of anodes used in electrolytic cells. Spacer clips of the invention provide uniform electrode positioning and spacing and improved protection against direct anode-to-cathode contact during placement of the cathodes and operation of the electrolytic cells.
In hydroelectrometallurgy, the electrodeposition of metals from electrolytes onto cathode starting sheets necessitates the positioning of anodes which are not consumed in the process on each side of the cathodes substantially coextensive with the cathodes. Touching of adjacent cathodes and anodes is a serious problem in the process and various means have been developed for separating and maintaining separate the anodes and cathodes from each other to prevent losses in current efficiency due to short-circuiting. For example, electrode header bars for suspending the cathodes and anodes in a spaced relationship, such as by notched supports, are commonly used and are effective for maintaining separation of the upper parts of the vertically disposed electrode plates. However, if the header bars are not rigidly attached to bus bars, the lower parts of the electrodes are free to move laterally and, unless this movement is restrained by the use of ancillary spacers, irregular deposition of metal with eventual short-circuiting, or even immediate short circuiting, may occur. In processes requiring frequent removal of cathodes from the electrolytic cells, rigid attachment of the header bars of these cathodes to bus bars necessitates considerable repetitive labour and impeded productivity and is thus preferably avoided. Anodes may be rigidly attached to the bus bars or may be suspended freely.
The framing of electrode plates with insulating material sufficiently thick to prevent electrical contact of adjacent anodes and cathodes, particularly with accumulated deposits of metal on the cathodes, has proven impracticable and uneconomic. The frames on the anodes tend to snag cathodes that are being immersed into or removed from the electrolyte. Also, such frames render ineffective much of the area of the electrodes. Guide strips have been set in cell side walls, but these also render considerable electrode area ineffective, require costly tank construction, and interfere with free circulation of electrolyte.
The attachment of small insulators directly to electrodes is well known. For example, the use of porcelain or plastic buttons inserted in the lower part of the anode, which is generally removed from the electrolyte less frequently than the cathode, is known. In that the buttons are small in size, the buttons advantageously render inactive only a small part of electrode surface but, due to frequent breakages, particularly during placement and removal of cathode sheets, frequent shutdowns have proven necessary for correcting short-circuiting.
U.S. Pat. No. 2,868,711 discloses the separation of the lower parts of anodes and cathodes by the placement of horizontal insulating rods supported loosely at their ends in structures attached to cells such that the weight of the rods presses the anodes into desired vertical alignment while permitting limited lateral movement of the anodes. Insertion of the horizontal rods through openings in the tank side walls can only be carried out when the electrolyte has been removed from the cell and, accordingly, this technique is not compatible with continuous process in which the tanks remain filled with electrolyte.
U.S. Pat. No. 2,872,406 discloses the separation of adjacent electrodes by the use of a rectangular frame made of styrene acrylonitrile copolymer to encase each anode by rigid vertical rods on each side of the anode. This apparatus serves functions other than the separation of anodes and adjacent cathodes and has proven too complex for continuous cathodic deposition of metals from electrolytes. In addition, this apparatus considerably reduces effective electrode surface area.
U.S. Pat. No. 2,995,507 teaches the use of vertically suspended helical strips of plastic with upper and lower ends connected to rigid bars suspended loosely between anodes and cathodes. These structures are non-conductors of electricity and are made of material with a specific gravity slightly greater than that of the electrolyte. This arrangement provides good utilization of electrolyte space and electrode area but serious disadvantages are complexity of design and difficulty in placement of cathodes between adjacent anodes.
Co-pending Canadian Pat. application No. 127,301 discloses a spacer clip which substantially overcomes the foregoing disadvantages of known electrode spacers. The spacer clip disclosed is adapted for attachment to the bottom of a vertically suspended anode sheet and comprises a wedge having a pair of opposed, spaced apart wings extending from each face of the wedge with outer faces initially diverging from the apex of the wedge and thence converging towards each other, whereby said wings can be flexed towards and away from each other. Longitudinal recesses are formed on opposite sides of the wedge for engagement with opposed edges of a slot in the anode sheet. In an electrolytic cell assembly comprising an arrangement of alternating suspended anodes and cathodes, each anode has at least one elongated vertical slot formed in its bottom edge. When a spacer clip is inserted in this slot, the wings of the spacer clip as described maintain substantially equal and parallel spacing of the lower ends of the anode and adjacent cathodes. Spacing of the upper ends of the electrodes may be maintained by known means such as the resting of the ends of supporting header bars in notches in bus bars and insulators. Such fixed, upper end spacing with bottom-mounted spacer clips generally provides effective separation of anodes and cathodes to eliminate short-circuiting in situ and to prevent losses in current efficiency.
In processes such as the electrolytic deposition of zinc on aluminum cathodes, the cathodes are cyclically removed from the electrolytic cells for separation of zinc and returned to the cells. It is customary to remove a portion of the cathodes from a cell without interrupting electrodeposition on the remaining cathodes in the cell. If removal and replacement of cathode sheets is carried out carefully, no difficulties will arise. However, during the raising or lowering of a set of cathodes, accidental swaying may occur, causing one or more cathodes to touch one or more anode header bars. The resulting short circuit damages the anode, even to the extent of burning off the header bar. Also, during the lowering of a set of cathodes, the entry of each cathode between a pair of anodes must be carefully guided to avoid contacts which damage electrode surfaces and which cause short-circuiting.